Difference between LPAR and VIO Server

December 31st, 2008

Often there is confusion between LPAR and VIO Server. The article is an attempt to clarify the difference between the two.

LPAR

LPAR as you all know is Logical Partition which is supported by IBM servers. During creation of LPAR CPUs, Memory and IO slots are provided to the partition from free pool of these resources. An LPAR acts as an independent server and is able to run AIX Operating System or Linux Operating Systems. In a physical server there can be many LPARs and corruption of one LPAR does not affect working of other partitions.

In case of LPAR the main security features are:

  1. Protection against inter-partition data access. Means one LPAR can not access data of another LPAR. Partitions will be able to access data from another LPAR only like it will be done when these are individual machines. Means no partition can cross its boundaries.
  2. If one LPAR fails, others keep running as such without fail.
  3. The resources are used fairly by LPARs. No partition can use PCI bus etc indefinitely.

VIO Server

VIO server is a special case of LPAR. In this the IOs are all virtual and provided to the partitions on VIO Server. Means IO slots, CPUs and Memory are all virtual. So, how is this done? This all is done through global firmware of Partition.

The two major functions provided by VIO Server are:

  1. Shared Ethernet Adapter.
  2. Virtual SCSI.

Shared Ethernet Adapter (SEA)

Shared Ethernet Adapter runs in the VIO Server. Its work is to route network traffic from partitions within VIO server to the real Ethernet adapter. Hence it acts as Layer 2 switch.

The major advantage of SEA is that partitions within VIO server can communicate in-between themselves as well as to the outside world. As if now up to 18 VLANs are supported on a single interface.

Virtual SCSI Devices (VSCSI)

The partitions within VIO Server don’t have physical disks. These have virtual disks and these virtual disks are implemented through Virtual SCSI services of VIO Server. The partitions within VIO server have access to the real storage through Virtual SCSI service. The partitions see these virtual SCSI disks as real disks. SAN, SCSI and RAID are all supported for VIO SCSI disks.

VIO Server is not used much in production environments. The reason behind this is that, if suppose this LPAR acting as VIO Server gets corrupted, all of the partitions working within VIO Server go down.

For more information on LPAR and VIO server read out the book SG24-7039-02 which is freely available from redbooks.ibm.com.

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